They will use as much cable as possible and when mowing the lawn, will have to make large turns. The towed array is rated with a static depth, so the dynamic load of the towed speed and turn is important. Due to the time required, they will not raise and lower the array when turning.

The distance between the parallel tracks is a function of the overlap at depth.

There are also Bluefin 21's in use.

They may also be towing a magnetometer, or multiple beam sonar array to image the bottom. I am sure if Ocean Shield isnt, others are.

Agreed. Doppler signatures were used for ELT locating by satellite before GPS's were integrated with ELT's. The relative doppler shift is a tenth of the under water case.

The lower duty cycle ping pulse will make it challenging. A fellow on the Reddit MH370 group used matlab to find a 0.4 millisec slowing down during a playback of 20 seconds of pings from a news broadcast. Lets put Inmarsat on the case.

Due to the time required, they will not raise and lower the array when turning.

Ocean Shield reels the TPL in to to a shallower depth when turning and then lowers it again. They in fact heard one of the first pings at a shallower-than-cruise depth after a turn. Turns take around three hours.

I am reliably informed that in fact the SAFE Act (Safe Aviation and Flight Enhancement) bill has not yet been introduced. It is in the process of being revised, extended and/or upgraded by certain relevant legislative staffs. It is my understanding that with respect to similar measures introduced in prior Congresses, committee hearings were not held. Of course the state of facts about what happened with the recorders on the Malaysian T7 is as yet indeterminant. It would be a wiser course not to legislate a mandate for FAA to amend all type certificates until such time as the (reasonably) full impact of this on-going event has been assessed and understood. At the very least, when it comes to aeronautical technology as the subject of Congressional action....one can always hope.

Last edited by WillowRun 6-3; 9th Apr 2014 at 17:11.
Reason: Cross - reference to prior post on same subject, for clarity

" 'It looks like the signals we’ve picked up recently have been much weaker than the original signals we picked up, so that means probably we’re either a long way away from it, or in my view more likely, the batteries are starting to fade and as a consequence, the signal is becoming weaker,' he [Angus Houston] warned.

'So we need to, as we say in Australia, make hay while the sun shines.' "

I am reliably informed that in fact the SAFE Act (Safe Aviation and Flight Enhancement) bill has not yet been introduced. It is in the process of being revised, extended and/or upgraded by certain relevant legislative staffs. It is my understanding that with respect to similar measures introduced in prior Congresses, committee hearings were not held . . .

Reliably informed? You're a lawyer - right? The SAFE Act was introduced and referred to committee twice before (2003 and 2005) and died there. A first year summer clerk could have told me no such act has been "introduced" this year. No need for any inside baseball here - please.

Let's not use big words to state the obvious - or what is otherwise breakfast table newspaper information . . .

While the most recent JACC media release at the moment I am typing advises that Haixun 01 and Echo are at the southern end of the underwater search area, with Ocean Shield at the northern, the current display of Echo position, track, and speed made good on marinetraffic.com shows Echo making 15.5 knots on a 37 degree course appearing to aim very closely at Ocean Shield's current position.

Meanwhile Haixun 01 shows as 16.7 knots on course 333, having made much progress toward the current surface search area.

They may never say this, but the disposition (and transit speeds, which are inconsistent with acoustic search) of the ships suggests to me that the much-discussed Chinese pinger contact is no longer being prosecuted, and that Echo may be transitting for sidescan sonar or other service at the site of the Ocean Shield contacts.

There was nothing "sudden" about their progress in the search. This search has been going on for over a month. We in the public are not priviy to all of the details of what they consider, what they reject, and what their cueing and trigger information have been.

Part of what they are doing involves the process of elimination, and making the most of such clues as are available. If we let the drama infested media influence our understanding of this search, we can fall into the trap of assigning traits like 'sudden' to events that unfolded over time for the search team and various national authorities.

They were indeed searching huge areas, but the areas have been shrinking every few days. Nothing strange, nothing sudden.

What took a lot of people by surprise (myself included) was the public announcenment that the early searches in the South China Sea and Malucca Straits needed to be abandoned, and a search far off the coast of Australia in the middle of nowhere granted precedence.

As I understand the background of this search, the indicators that this was a better course of action did not arrive suddenly, but were derived from the process of vetting and analyzing the sparse information available. No drama: plodding detective work.

I thought it was the 'boring' work of ongoing detail analysis of the Inmarsat data coupled with more refined analysis of 777 performance characteristics that fit to the pattern of known arcs and dopplers that lead to deploying listening assets in the 'small arc' where Haixun 01 and Ocean Shield were operating.

It seems quite likely that after a lot more hard analysis of the acoustic data they will have localised a reasonable search area and then in several weeks will have found the wreckage with the side scan sonar.

Nothing particularly sinister in all of this analysis and thinking taking a lot of time.

There was something that led them to that spot in the Indian Ocean, some clue or intelligence that meant Ocean Shield heard the first pings on the very day the black box batteries were due to start weakening. Something told them to look there... I doubt we will ever find out!

It was the realisation that the aircraft was flying lower.

The resulting faster IAS, slower TAS, and thus slower groundspeed - and the resulting shorter range - meant that the search location had to move along the last ping-ring towards the northeast. Simple, really.

What we don't yet know, is why they suddenly realised that the aircraft flew at low-level.

P.S. If someone can post the fuel-burn/altitude tables for 1,000' and 10,000', it would be fairly easy to calculate roughly how low it flew.

The resulting faster IAS, slower TAS, and thus slower groundspeed - and the resulting shorter range - meant that the search location had to move along the last ping-ring towards the northeast. Simple, really.

What we don't yet know, is why they suddenly realised that the aircraft flew at low-level.

P.S. If someone can post the fuel-burn/altitude tables for 1,000' and 10,000', it would be fairly easy to calculate roughly how low it flew.

I think the reasoning was the reverse. Assume last ping was at out-of-fuel. That gives a fuel burn rate which can then be reverse looked up to find the cruise levels/speeds that would result in that burn rate now fit those speeds/levels to the several INMARSAT rings the one that most closely fits tells you where on the final ring the aircraft was out-of-fuel. Use simulation of aircraft behavior when fuel is out at that level/speed, then generate a new search area. Pingo